The present invention relates to an electronic control unit.
A typical electronic control unit includes a casing and an electronic circuit substrate accommodated in the casing. The casing is waterproofed in various ways (see, for example, Japanese Laid-Open Patent Publication No. 2005-150633). Nonetheless, if the electronic control unit is installed in, for example, a vehicle having limited space, it is necessary to further improve the resistance to water of the casing for space efficiency in the vehicle.
More specifically, if the electronic control unit is installed at a position where the casing is likely to be soaked, or completely immersed, in water in certain traveling states of the vehicle, the water resistance of the typical waterproof casing may be insufficient. For example, the water may enter the casing from the interface between the casing and a connector terminal that extends through the casing. Thus, to further increase the water resistance of the casing of the electronic control unit, it is necessary to waterproof the portion in which the connector terminal is provided.
However, the portion in which the connector terminal is installed cannot be sealed by a seal member such as an O-ring, which is used for sealing the gap between the body of the casing and a lid that blocks the opening of the casing. It is thus necessary to apply a liquid seal agent to the basal end of the connector terminal, which extends through a side wall of the casing and projects into the space in the casing. The liquid seal agent is solidified in a raised form using surface tension produced by the seal agent in such a manner that the seal agent is fixed to the basal end of the connector terminal. Such raising (potting) of the seal agent is extremely complicated. Further, it is difficult to form a stable waterproof layer by this procedure.